CAUSAL RELATIONAL REASONING OF 5 TH GRADERS USING DENSITY IN EXPLAINING FLOATING-SINKING PHENOMENA

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1 CAUSAL RELATIONAL REASONING OF 5 TH GRADERS USING DENSITY IN EXPLAINING FLOATING-SINKING PHENOMENA A. Zoupidis 1, D. Pnevmatikos 1, A. Spyrtou 1 and P. Kariotoglou 1 tzoupidis@gmail.com, dpnevmat@uowm.gr, aspirtou@uowm.gr, pkariotog@uowm.gr 1 School of Education, University of Western Macedonia, Florina, Greece Abstract: The aim of the present study was to investigate if students use causal relational reasoning using density in explaining floating/sinking (F/S) phenomena before, during and after the implementation of a Teaching/Learning Sequence (TLS). The study is part of a cross-national research-based curriculum project on Materials Science. One of the theoretical bases for the design of the TLS was focused on a model-based learning approach. The TLS was designed and developed by researchers working in close collaboration with school teachers comprising a University School partnership. Its implementation took place in two science classrooms of forty-one 5 th graders (mean age 10.9; SD =.376) in total. Participants answered 5 tasks (pre, during, just after and seven months after the implementation) on explaining F/S phenomena using the concept of density. A significant shift on participants conceptual understanding was evident; participants grasped the scientific concept of density after the intervention. In addition, it seems that a significant number of participants could successfully explain F/S, using causal relational reasoning. Finally, participants who managed to use density in a causal relational reasoning had a significantly better understanding of density as a property of materials than those who used density in a causal linear reasoning. Keywords: Model-based learning, Causal relational reasoning, Concept acquisition, Density, Floating/Sinking phenomena BACKGROUND, FRAMEWORK, AND PURPOSE Model-based reasoning can be thought of as a continuum in which teachers begin with students basic representational capacities and try to end up near the practices of scientists (Nersessian, 2008). An important constrain in this transition is the narrow range of students causal models. Most of them tend towards simple causal models in explaining phenomena. For instance, when they try to explain F/S of an object, they focus only on the object, giving answers such as it sinks because it is heavy (Kohn, 1993). However, many concepts and theories in science depend on substantially more complex causal models (Perkins & Grotzer, 2005). Causal relational reasoning, being such a complex model, in the case of F/S provides interpretations such as if an object has bigger density than a liquid then it sinks. Perkins & Grotzer (2005) argued that cultivating greater complexity in students causal models leads to better understanding of phenomena and relevant concepts that are used to interpret them. Moreover, there is a considerable agreement that density is an abstruse notion for students. Students, before being exposed to the systematic teaching at schools, have already developed a conceptual framework about matter and material kind, which differs from the scientific one (Smith, Snir & Grosslight 1992; Hardy et al. 2006; Wiser & Smith 2008). Within students conceptual framework, the concepts of weight and density are undistinguished

2 (Fassoulopoulos, Kariotoglou & Koumaras, 2003). Moreover, students by referring to the density of an object, they focus on only one feature of the object, either on the weight, the size or the shape, (Smith, Snir & Grosslight, 1992). Smith et al. (1992) also argued that the necessary condition to conclude that students have grasped the concept of density, in an elementary level, is to realize that the heaviness of the kind of material is a property of that material. In addition, they claim that this is a prerequisite in order to argue that students can distinguish the concepts of weight and density. RATIONALE Although the concept of density is considered among the most difficult concepts for primary school students, there is little empirical evidence of (TLSs) (Μéheut & Psillos 2004), that use the model-based reasoning to help students to abandon the constraints of the linear causal reasoning ( Perkins & Grotzer, 2005). In this study, we were keen to answer the following research questions: (a) In what extent do students acquire density as a property of materials? (b) Do students use causal relational reasoning in explaining F/S? (c) Does the use of complex causal reasoning help students to understand the concept of density? For this purpose a five unit TLS on density as a materials property (Spyrtou, Zoupidis & Kariotoglou, 2008) has been developed. Fig. 1: The visual dots-in-a-box model of several materials More specifically, in the 1 st unit of the TLS, participants were introduced to the technological problem of the salvage of the Sea Diamond s shipwreck through a video which included a description of the accident and a discussion about its environmental consequences. Furthermore, the participants were familiarized with F/S phenomena and the relevant concepts through several activities, such as real experiments, working in a Predict-Observe- Explore (POE) approach. In the 2 nd unit, the participants working in groups, followed the POE approach in real and simulated experiments in order to identify and test possible variables that affect F/S, for instance, the weight of an object and the kind of the liquid s or the object s material. In the 3 rd unit the participants were introduced to a visual model of density as a property of material, the dots-in-a-box model (Smith, et al., 1992, Figure 1). Using this representation in relevant simulated experiments we expected that the participants would acquire a causal relational reasoning (Perkins & Grotzer, 2005) in order to explain and predict F/S phenomena for homogenous objects. In the 4 th unit, participants used the visual model to come to a conclusion about the F/S of two-materials composite objects, for instance a bottle filled with air or a bottle filled with water. By doing this, we aimed to help participants to understand that the density of a composite object, which consists of two materials, lies between the densities of the two materials. Finally, in the 5 th unit, participants had the opportunity to work in groups in a simulated environment and to investigate the F/S of the Sea Diamond cruise ship, in order to argue about its salvage. METHOD

3 This study was conducted in two 5 th grade science classrooms. Forty one 5 th graders (mean age 10.9, SD =.38) participated in the study. Each of the five units of the TLS lasted for 2 teaching periods of approximately 80 min in total. The implementation took place during normal daily courses and the female class teacher had great experience in teaching science. Data Collection: Data were collected from multiple sources. For the sake of conciseness, in this paper we will be limited in presenting the results only of the analysis of the learning of density as a property of materials (Tasks 1, 2 and 3), as well as the use of causal relational reasoning in explaining F/S (Tasks 4 and 5) of the pre (just before implementation), interim (between 4 th and 5 th unit), post (just after implementation) and post-post (seven months after implementation) phases of evaluation. More specifically, task 1 asked participants to write a sentence including the words density and material. Task 2 asked participants to choose and explain their choice, on which of two objects of the same amount and material, but of different shape has bigger density, or if they have the same density. Task 3 asked participants to choose and explain their choice, on which of two objects of the same material, but of different size has bigger density, or if they have the same density. In task 4 participants were asked to draw a big sphere and a small triangle in their final position in a liquid, taking into account the densities that are given in dots-in-a-box representation (sphere s material: two dots, triangle s material: six dots and liquid s material: four dots). They were also asked to explain their drawings. Finally, in task 5, participants were asked to choose and explain their choice, about the final position of two identical spheres in a liquid, taking into account the densities that are given in dots-in-a-box representation (object s A material: two dots, object s B material: three dots and liquid s material: four dots). The first choice was that the two objects are floating at the same level, the second that object B floats in a higher level than object A and the third choice is that object A floats in a higher level than object B. Tasks 1, 2 and 3 were addressed to participants in each of the four phases (pre, interim, post and post - post) of the TLS, while tasks 4 and 5, only in the last three phases. Coding: Answers in tasks 1, 2 and 3 were classified in four categories, and in tasks 4 and 5 in two categories, by two independent judges, with 85% agreement which after a discussion was increased to 100%. The same categories were used in the tasks 1, 2, and 3. Phenomenological, incomplete or no answers were classified in the no answer category (0). Answer s that accepted density as dependent on the object s size, (e.g. the big object has bigger density ), were classified in the category extensive idea and they were credited with one (1). Answers that accepted density as a property of materials and dependent on the object s size, (e.g. the objects have the same density because they are made from the same material and the same quantity ), were classified in the category transitional idea and they were credited with two (2). Finally, answers that considered density as a property of materials, (e.g. both objects have the same density because they are from the same material ), were classified in the category intensive idea and they were credited with three (3). The means of the classification in these three tasks were calculated and rounded for each student. Answers that were based on causal relational reasoning to explain F/S, (e.g. object A floats because its density is smaller than the liquid s and object B sinks because its density is higher than the liquid s ), in task 4, were classified as causal relational and credited with one (1). Additionally, answers that used causal linear reasoning, (e.g. object A will float because it is light and object B will sink because it is heavy ), were classified as causal linear and were credited with zero (0). Answers that used causal linear reasoning in task 5, ( e.g. they both float because they are light ), were classified as causal linear and were credited with zero (0). Additionally, answers that used causal relational reasoning to explain F/S, (e.g. I choose the third picture because both objects have smaller density than the liquid and object B has bigger density than object A ), in task 5, were classified as causal relational and were

4 credited with one (1). The means of the categorization in the last two tasks were also calculated and rounded for each student. RESULTS Table 1 presents the participants progress in understanding the concept of density as a property of materials. As it was expected, the number of participants that considered density as a property of materials increased significantly after the first and second part of our implementation (interim and post measure), while the number of participants answering irrelevant, phenomenological or incomplete answers decreased significantly from the pre to the post phase of evaluation (Wilcoxon Signed-Rank Test, z=4.8, p <.001). Furthermore, the pattern of answers remained unchanged from post to post-post evaluation (Wilcoxon Signed- Rank Test, z=.29, p =.770). Nevertheless, a small though considerable number of participants were still assuming that density is an extensive quantity (category 1). Table1. Frequencies of participants found in each category in each time-point concerning learning of density as a property of materials Tasks 1, 2 and 3 Time-points Categories pre interim post post-post 3: Density as a property of materials (intensive idea) : Density as a property of materials and dependent on the shape, weight or size of the object (transitional idea) : Density dependent on the shape, weight or size of the object (extensive idea) : Phenomenological, incomplete or no answers Total answers The results concerning participants explanations of F/S phenomena are shown in table 2. These results are based on participants answers in Task 4 and 5, which were conducted only in interim, post and post-post phase of evaluation. Table2. Frequencies of participants found in each category in each time-point concerning participants explanations of F/S phenomena Tasks 4 and 5 Time-points Categories interim post post-post 1: Use of density in a causal relational reasoning : Use of density in a causal linear reasoning Total

5 A considerable number of participants (seventeen out of forty-one) were able to use density in a causal relational reasoning after the first phase of our implementation in the intermediate phase of evaluation (see Table 2). This number was significantly increased in the end of the TLS where almost one out of two participants used density in a causal relational reasoning (Wilcoxon Signed-Rank Test, z=2.7, p <.05). However, this improvement lost at the post-post time point, seven months later, and participants started using density in a linear reasoning again (Wilcoxon Signed-Rank Test, z=2.4, p <.05). Mann-Whitney non-parametric analysis was used in order to test our hypothesis that cultivating causal relational reasoning in explaining F/S phenomena could lead to better understanding of density as a property of materials. More specifically, we divided our participants in two groups; those who in each time-point understood and used causal relational reasoning and those that used causal linear reasoning in explaining F/S. For each group of participants we calculated the means corresponding to their conceptual understanding of density as a property of materials. As we expected, significantly more participants who used causal relational reasoning, understood density as a property of materials, than participants who used causal linear reasoning in interim ( p =.040), post ( p =.007), and post-post (p =.001) phase of testing. CONCLUSIONS The results showed statistically significant increase of the participants who understood density as a property of materials, which remained stable seven months later (Table 1). Furthermore, there were a considerable number of participants who used density in a causal relational reasoning to explain F/S phenomena (Table 2). In parallel, the number of participants who used causal relational explanations in the post phase of evaluation significantly increased, in comparison with the interim one. One possible explanation for this improvement could be the use of the Sea Diamond s cruise ship simulation, in the 5 th unit. In this unit participants used the Sea Diamond cruise ship simulation in order to investigate the conditions under which a ship sinks and floats, in the frame of the technological problem solving of the salvage of the sunken ship. Nevertheless, this improvement did not remain seven months later. An explanation of that could be the short period given to such activities, that is, only a part of the last unit of the TLS. Last but not least, we noticed that participants who managed to use density in a causal relational reasoning had a better understanding of density as a property of materials, in a statistically significant degree, than those who used density in a causal linear reasoning. We consider that this result is in favor of Perkins & Grotzer (2005) claim, that cultivating complex causal reasoning can enhance participants concepts understanding. ACKNOWLEDGMENT Work presented in this paper has been supported by the EU through the ECRDG in the project Materials Science University-school partnerships for the design and implementation of research-based ICT-enhanced modules on Material Properties, Science and Society Programme, FP6, SAS6-CT

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